Strain-rate and off-axis loading effects on the fibre compression strength of CFRP laminates: Experiments and constitutive modelling

A series of dynamic longitudinal compression tests have been performed on cross-ply IM7/8552 specimens cut at different off-axis angles to produce different combinations of compression and shear stresses. Together with results from previous quasi-static tests of the same kind, quasi-static and dynamic fibre kinking failure envelopes have been obtained using classical laminate theory. This new experimental data has been compared against predictions from the leading fibre kinking theories, made rate-dependent by using rate-dependent in-plane shear properties, and show that, while they can accurately predict the effects of strain rate on the uniaxial compression strength, they are unable to capture the effects of shear, neither at quasi-static nor dynamic rates. Instead, a simpler more phenomenological approach is proposed to predict the rate-dependent fibre kinking strength of FRP laminates under multi-axial loads until the micromechanics can be more accurately described.